117
x² - xy +x - xy² + y³ - y² = (x² -xy) + (y³- xy²) + (x² - y²) =
= x(x - y) + y²(x - y) +(x - y)(x + y) = (x - y)(x + y² +x + y) = (x - y)(2x + y² + y)
x²y + x + xy² + y +2xy +2 = (x²y + xy² +2xy) + ( x + y +2) =
= xy(x + y +2) + ( x + y +2) = ( x + y +2)(xy +1)
720
4 - x( x+8) = 11 - x²
4 - x² - 8x = 11 - x²
- x² + x² - 8x = 11 - 4
- 8x = 7
8x = - 7
x= - 7/8
4x( 3x - 1) - 2x( 6x + 8) = 5
12x² - 4x - 12x² - 16x = 5
- 20x = 5
20x = - 5
x = - 0,25